I've recently been in negotiation with Pirelli about some tyres which had a manufacturing fault, and which was only recognised at 12,000 miles or so.
A technician from their lab called me today, and he actually said that because I'd been so pleasant and patient through, then they'd refund me 100% rather than reduce it due to wear during the period the tyres were used.
He said almost everyone he deals with shouts, screams, and makes bold claims about suing Pirelli unless they get exactly what they want, and so a more relaxed approach is a relief to them. They're only human afterall, and so they're more inclined to go the extra mile if you're pleasant with them.
A big thumbs up to Pirelli - just waiting to see how long it takes the tyre fitting centre to actually send me a cheque now!!